1. Field of the Invention
The present invention is generally directed to cochlear implant electrode leads, and more particularly, to a cochlear implant electrode lead having a cross-section with a variable height.
2. Related Art
A cochlear implant allows for electrical stimulation signals to be applied directly to the auditory nerve fibers of a patient, allowing the brain to perceive a hearing sensation approximating the natural hearing sensation. These stimulation signals are applied by an array of electrodes implanted in the patient's cochlea.
The electrode array is connected to a stimulator unit which generates the stimulation signals for delivery to the electrode array. The stimulator unit in turn is operationally connected to a signal processing unit, which contains a microphone for receiving audio signals from the environment. The signal processing unit processes the audio signals to generate control signals for the stimulator unit.
FIG. 1 shows a diagramatically-representative cross section of a cochlea 50. Shown there are three channels, known as the scala tympani 51, the scala media and the scala vestibuli in use, an electrode lead containing the electrode array is inserted into the scala tympani 51 and caused to make contact with the modiolar wall of the scala tympani 51, close to the ganglion cells within the modiolus.
It is desirable that electrode contacts of the electrode array are positioned as close to the ganglion cells as possible. The spiral ganglion cells lie in the bone or modiolus, adjacent to the inside wall of the scala tympani 51 as shown in FIG. 1. Conventionally, after implantation, the electrode array consisting of electrode contacts should hug the modiolar wall (or inside wall of the scale tympani). When the electrode array is positioned so as to hug the modiolar wall, the electrode contacts are on the medial side of the lead.
In order to facilitate close contact of the electrode contacts of the electrode array, the carrier material forming the electrode lead is molded to assume a specific pre-curved shape having memory. Therefore the natural resting position of the lead has a carved distal lead tip. When the array tip is straightened (for example by stylet or insertion tube), the tip stores elastic energy which exerts a force tending to restore the lead to its originally-molded curved shape. When the lead is implanted, the medial side of the lead hugs the modiolar wail and thus achieves a medial electrode array placement.